1. Field of the Invention
The present invention relates to ink jet printers of the type which routinely fire ink droplets over a maintenance station to insure optimal drop control while printing and more particularly to controlling the dispersion of smaller ink droplets during maintenance.
2. Description of the Related Art
Ink droplet firing, as a part of a maintenance algorithm, occurs to clear the print head nozzles of contamination or to prevent ink chemistry changes at the nozzle openings due to crusting, viscosity changes, or separation of ink constituents. A common problem is the fragmentation of the ink droplet during jetting. Fragments of various sizes break from the tail of an ejected drop. The smaller fragments quickly lose momentum and may never reach the waste ink control surface of the maintenance station. The trajectory of the smaller fragments is altered by aerodynamic drag. They slow down losing momentum, thus becoming subject to uncontrolled air currents within the printer. These uncontrolled droplets behave as if buoyant until the electrostatic force of nearby surfaces attract the droplets. (Fragmented droplets, which are also controlled by aerodynamic drag, will be referred hereafter as xe2x80x9cmistxe2x80x9d.) This results in misting on the printed page, discoloring of features inside the printer, and, possibly, discoloring of articles surrounding the printer due to contaminated air exhaust.
A traditional method of controlling ink misting during maintenance is to provide a surface near the nozzle openings for ink mist and residue to accumulate. Ideally, the distance from nozzles to accumulating surface (gap height) would be less than the xe2x80x9cthrow distancexe2x80x9d, which is defined here as the distance a fragmented droplet travels before momentum is lost. Unfortunately, the distance required for the residue accumulation resulting from these maintenance techniques and the necessary clearance between the residue and the printhead is substantially greater than the throw distance of many of the smaller particles.
The present invention utilizes an accumulating surface at throw distances that reasonably satisfy the large gap requirements of mist accumulation and clearance, while controlling the location of mist accumulation. This is accomplished with the addition of an air flow which increases droplet momentum, and/or forms a barrier, or xe2x80x9cair curtainxe2x80x9d to confine the mist to a corridor between the print head and a waste ink accumulating surface.
The invention comprises, in one form thereof, a process of confining and controlling waste ink jetted from an ink jet printer print head toward an adjacent waste ink accumulating surface by forcing air past the print head lateral surfaces and toward the accumulating surface to create an air curtain around a corridor from the print head to the surface to thereby minimize the dispersion of ink mist from the print head.
An advantage of the present invention is that the boundaries of ink mist migration at both the louvers and spit wheel are controlled.
Another advantage is ink droplet momentum to a waste ink accumulating surface is maintained by an air flow.
Yet another advantage is ink mist is collected prior to the exhaustion of air from the printer.